CVE-2026-21434: webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule

CVE-2026-21434 · Severity: low · CVSS 3.1 · Published 2026-02-19

webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule in github.com/quic-go/webtransport-go

Technologies: github.com/quic-go/webtransport-go (Go). Vendors: Go.

Quick answers

Is CVE-2026-21434 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-21434 being exploited in the wild.
How severe is CVE-2026-21434?
Low severity, with a CVSS score of 3.1, published 19 February 2026.
Which products and versions are affected?
github.com/marten-seemann/webtransport-go (Go) SEMVER:introduced=0.3.0; github.com/quic-go/webtransport-go (Go) SEMVER:introduced=0,fixed=0.10.0, SEMVER:introduced=0.3.0,fixed=0.10.0.
Is there a fix for CVE-2026-21434?
Yes. github.com/quic-go/webtransport-go (Go): upgrade to 0.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-21434?
Check whether you run github.com/marten-seemann/webtransport-go (Go) or github.com/quic-go/webtransport-go (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/quic-go/webtransport-go (Go): upgrade to 0.10.0 or later
    go get github.com/quic-go/webtransport-go@v0.10.0

Affected products

  • github.com/marten-seemann/webtransport-go (Go) SEMVER:introduced=0.3.0
  • github.com/quic-go/webtransport-go (Go) SEMVER:introduced=0,fixed=0.10.0, SEMVER:introduced=0.3.0,fixed=0.10.0

Identifiers

  • CVE-2026-21434
  • GHSA-g6x7-jq8p-6q9q
  • GO-2026-4485

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